US President Barack Obama says he would be prepared to authorise another covert raid inside Pakistan against al-Qaeda or Taliban leaders.
In an interview with the BBC ahead of a visit to Europe, Mr Obama said he was mindful of Pakistan's sovereignty, but could not stand by and allow active plans by enemies of the US to come to fruition.
The head of al-Qaeda, Osama bin Laden, was killed in a raid by US forces earlier this month on a compound in the Pakistani city of Abbottabad.
Asked what he would do if one of al-Qaeda's top leaders, or the Taliban leader Mullah Omar, was tracked down to a location in Pakistan or another sovereign territory, he said the US would take unilateral action if required.
"Our job is to secure the United States," he said. "We are very respectful of the sovereignty of Pakistan. But we cannot allow someone who is actively planning to kill our people or our allies' people."